1. Field of the Invention
The invention relates to steering and/or stabilising device for motorised watercraft with at least two operating units comprising each a retractable steering and/or stabilising fin.
A motorised watercraft requires a steering device which is not only prompt, precise and light but also offers a minimal resistance to forward movement in the water.
The invention is based on the fact that any watercraft having a completely symmetrical keel and with balanced propulsive forces tends to keep a constant course when sailing if no extraneous forces such as wind, wave motion, current etc. intervene to change the direction of navigation. This is particularly true for fast motorised watercrafts with modern hulls having deep, V-shaped keel
Studies and trials have been carried out on steering devices having two operating units, each comprising a retractable fin and fitted outside the stern of the watercraft in symmetrical positions, one to the starboard side and the other to the port side, these steering fins being kept out of the water during navigation on course and being inserted alternatively and for different extents into the water on the starboard side or on the port side, only when a change of course is required.
2. Description of the Prior Art
A steering device of this type is known from the document EP 0518229 A1. Each unit of this known device comprises a steering fin attached on the outside of the transom and swinging up and down. A operating unit of this kind is showed in FIG. 1 of the accompanying drawings, in which the swinging steering fin mounted outside of the transom T is indicated with 2 and is actuated by a cylinder 1 located as well outside of the transom T.
This known kind of steering device yielded highly favourable results in trials, in which it was confirmed that a watercraft navigating without rudders showed no greater instability in maintaining a course than a watercraft provided with conventional rudders, and indeed revealed that steering fins immersed alternatively and for variable extents on the starboard side and on the port side, provided course maintaining and manoeuvring characteristics which were clearly not inferior to those of the conventional rudder systems, with the considerable advantage of causing no resistance to forward movement when the steering fins are retracted during on a constant course.
The known steering device of this kind was not generally applied because of the marked tendency to conservatism characteristic of marine design in general and because of the problems arising from the particular type of steering fins attached on the outside of the transom and projecting from the transom in an area which is normally used for bathing, particularly in leisure vessels. It was also feared that any collision with a quay when backing might damage the integrity of the steering means.
A known stabilising device of the kind mentioned above for motorised watercraft comprises two operating units located preferably in the middle zone of the watercraft, one to the starboard side and the other to the port side and the respective stabilising fins project in the water, placed transversely to the side.
The stabilising fins now known generate forces capable to oppose rolling effect opportunely rotating on a shaft similarly to the conventional rudders. The complicate system of the rotation does not permit except for large watercraft or for ship the possibility to be retractable when the stabilising effect of the fins is not required. This property of the known fins does not permit its application on small or medium size watercraft particularly if fast or planning because the of the excessive resistance in the forward advancement in the water.